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This article in SSSAJ

  1. Vol. 50 No. 1, p. 173-177
    Received: Jan 22, 1985



Soils at Prehistoric Agricultural Terracing Sites in New Mexico: II. Organic Matter and Bulk Density Changes1

  1. J. A. Sandor,
  2. P. L. Gersper and
  3. J. W. Hawley2



Soil changes initiated by prehistoric cultivation in a semiarid region of southwest New Mexico are still evident about 900 yr after cultivation ceased. Bulk density increases and reductions in organic C and total N were inferred by comparing cultivated soils with nearby, similarly developed uncultivated soils. Comparisons were also made between A horizons and sediment deposits accumulated upslope of recently fallen trees. These deposits are considered analogous to fresh agricultural terrace deposits just prior to cultivation. Depth of cultivation-induced changes varies but is generally limited to the upper solum. Mean bulk density of cultivated A horizons is 9 and 15% higher than that of uncultivated A horizons and recent sediment deposits, respectively. Cultivated soils are lower in organic C than uncultivated soils by 45, 38, and 32% in the A, BAt, and Bt horizons, respectively. The trend continues through the Bt horizon but is not statistically significant at p < 0.05. Recent sediment deposits tend to be higher in organic C than uncultivated soils and are 54% higher than cultivated A horizons. Total N data give results similar to that of organic C. The significant negative correlation between organic C and bulk density in uncultivated A horizons is not present in cultivated A horizons as values tend to group around a narrower range of lower organic C and higher bulk density values. The long-term degradation of these cultivated Mollisols is attributed to their sensitivity to disturbance.

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